Method and apparatus of transmitting ppdu in wireless communication system

ABSTRACT

A method is provided for transmitting a physical layer protocol data unit (PPDU) in a wireless communication system. For a first data stream associated with a first PPDU to be transmitted via a first channel, a wireless device includes a first data block, a first header indicating a first modulation and coding scheme (MCS), and a first physical layer service data unit (PSDU) in the first data stream. For a second data stream associated with a second PPDU to be transmitted via a second channel, the wireless device includes a second data block, a second header indicating a second MCS and a second PSDU in the second data stream. The wireless device performs a padding procedure to at least one of the first data stream and the second data stream, and transmits the first data stream and the second data stream by using the first PPDU and the second PPDU.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of co-pending U.S. patent applicationSer. No. 14/041,950 filed on Sep. 30, 2013, which is a continuation ofU.S. patent application Ser. No. 12/994,985 filed on Nov. 29, 2010 (nowU.S. Pat. No. 8,619,814 issued on Dec. 31, 2013), which is the NationalPhase of PCT International Application No. PCT/KR2009/002872 filed onMay 29, 2009, which claims the benefit of U.S. Provisional ApplicationNo. 61/057,640 filed on May 30, 2008, and which claims priority toApplication No. 10-2008-0058977 filed in the Republic of Korea on Jun.23, 2008. The entire contents of all of the above applications arehereby incorporated by reference.

BACKGROUND OF THE INVENTION

The present invention relates to a wireless local access network (WLAN),and more particularly, to a method and apparatus of transmitting aphysical layer convergence protocol (PLCP) protocol data unit (PPDU) ina WLAN.

With the advancement of information communication technologies, variouswireless communication technologies have recently been developed. Amongthe wireless communication technologies, a wireless local access network(WLAN) is a technology whereby super high-speed Internet access ispossible in a wireless fashion in homes or businesses or in a regionproviding a specific service by using a portable terminal such as apersonal digital assistant (PDA), a laptop computer, a portablemultimedia player (PMP), etc.

Ever since the institute of electrical and electronics engineers (IEEE)802, i.e., a standardization organization for WLAN technologies, wasestablished in February 1980, many standardization works have beenconducted. In the initial WLAN technology, a frequency of 2.4 GHz wasused according to the IEEE 802.11 to support a data rate of 1 to 2 Mbpsby using frequency hopping, spread spectrum, infrared ray communication,etc. Recently, the WLAN technology can support a data rate of up to 54Mbps by using orthogonal frequency division multiplex (OFDM). Inaddition, the IEEE 802.11 is developing or commercializing standards ofvarious technologies such as quality of service (QoS) improvement,access point (AP) protocol compatibility, security enhancement, radioresource measurement, wireless access in vehicular environments, fastroaming, mesh networks, inter-working with external networks, wirelessnetwork management, etc.

In the IEEE 802.11, the IEEE 802.11b supports a data rate of up to 11Mbps by using a frequency band of 2.4 GHz. The IEEE 802.11acommercialized after the IEEE 802.11b uses a frequency band of 5 GHzinstead of the frequency band of 2.4 GHz and thus significantly reducesinfluence of interference in comparison with the very congestedfrequency band of 2.4 GHz. In addition, the IEEE 802.11a has improvedthe data rate to up to 54 Mbps by using the OFDM technology.Disadvantageously, however, the IEEE 802.11a has a shorter communicationdistance than the IEEE 802.11b. Similarly to the IEEE 802.11b, the IEEE802.11g realizes the data rate of up to 54 Mbps by using the frequencyband of 2.4 GHz. Due to its backward compatibility, the IEEE 802.11g isdrawing attention, and is advantageous over the IEEE 802.11a in terms ofthe communication distance.

The IEEE 802.11n is a technical standard relatively recently introducedto overcome a limited data rate and throughput which has been consideredas a drawback in the WLAN. The IEEE 802.11n is devised to increasenetwork speed and reliability and to extend an operational distance of awireless network. More specifically, the IEEE 802.11n supports a highthroughput (HT), i.e., a data processing speed of up to 540 Mbps at afrequency band of 5 GHz, and is based on a multiple input and multipleoutput (MIMO) technique which uses multiple antennas in both atransmitter and a receiver to minimize a transmission error and tooptimize a data rate. In addition, this standard may use a coding schemewhich transmits several duplicated copies to increase data reliabilityand also may use the OFDM to support a higher data rate.

With the widespread use of WLAN and the diversification of applicationsusing the WLAN, there is a recent demand for a new WLAN system tosupport a higher throughput than a data processing speed supported byIEEE 802.11n. However, an IEEE 802.11n medium access control(MAC)/physical layer (PHY) protocol is not effective to provide athroughput of 1 Gbps or more. This is because the IEEE 802.11n MAC/PHYprotocol is designed for an operation of a single station (STA), thatis, an STA having one network interface card (NIC), and thus when aframe throughput is increased while maintaining the conventional IEEE802.11n MAC/PHY protocol, a resultant additional overhead is alsoincreased. Consequently, there is a limitation in increasing athroughput of a wireless communication network while maintaining theconventional IEEE 802.11n MAC/PHY protocol, that is, a single STAarchitecture.

Therefore, to achieve a data processing speed of 1 Gbps or more in thewireless communication system, a new system different from theconventional IEEE 802.11n MAC/PHY protocol (i.e., single STAarchitecture) is required. A very high throughput (VHT) system is a nextversion of the IEEE 802.11n WLAN system, and is one of IEEE 802.11 WLANsystems which have recently been proposed to support a data processingspeed of 1 Gbps or more in a MAC service access point (SAP). The VHTsystem is named arbitrarily. To provide a throughput of 1 Gbps or more,a feasibility test is currently being conducted for the VHT system using4×4 MIMO and a channel bandwidth of 80 MHz.

The IEEE 802.11a standard uses a channel bandwidth of 20 MHz at a 5 GHzband. According to this standard, up to 13 channels can be used, whichmay differ from one country to another. In addition, the IEEE 802.11nstandard uses channel bandwidths of 20 MHz and 40 MHz at the 5 GHz band.In this situation, the newly proposed VHT system can use a channelbandwidth of 80 MHz or more at the 5 GHz band according to two methodsdescribed below.

In a first method, a channel bandwidth of 80 MHz or more is used, and achannel in use includes a plurality of non-contiguous subchannels.Subchannels are non-contiguous when a different band is allocatedtherebetween. The channel used in this method can be referred to as an“aggregation channel”. A plurality of 20 MHz subchannels can be groupedto ensure an 80 MHz aggregation channel required in the VHT system.Advantageously, this method can be a practical solution that considers acurrent channel usage at the 5 GHz band which is commercialized andrealized at present. However, it is not easy to manage thenon-contiguous subchannels according to a single communication protocol,and channel efficiency may differ from one subchannel to another when asubchannel spacing is great. Therefore, this method is not mucheffective.

In a second method, a channel in use includes a plurality of contiguoussubchannels. The bandwidth of the channel may be 80 MHz or more. Thechannel used in this method can be referred to as a “bonding channel”.20 MHz subchanncls contiguous to one another are grouped into 4subchannels to ensure a 80 MHz bonding channel required in the VHT WLANsystem. Since this method concurrently manages a plurality of contiguoussubchannels, there is an advantage in that channel management can beeffectively achieved and a channel characteristic is not significantlydifferent from one subchannel to another.

However, the VHT system using the bonding channel can be adopted bysolving a problem of coexistence with a WLAN system using theconventional 5 GHz band, that is, the IEEE 802.11a and IEEE 802.11n WLANsystem. That is, if the coexistence problem with the IEEE 802.11a andIEEE 802.11n WLAN system currently commercialized is not solved, it isdifficult to adopt the VHT system using a continuous channel bandwidthof 80 MHz or more at the 5 GHz band. Consequently, the VHT system usingthe continuous channel bandwidth of 80 MHz or more inevitably has tocoexist with the conventional IEEE 802.11a and IEEE 802.11n WLAN system.Therefore, there is a need to solve the coexistence problem with theconventional WLAN system.

SUMMARY OF THE INVENTION

The present invention provides a method and apparatus of transmitting aphysical layer convergence protocol (PLCP) protocol data unit (PPDU) forcoexistence with a legacy station (STA).

The present invention also provides a method and apparatus oftransmitting a PPDU supporting high throughput.

The present invention also provides a method and apparatus oftransmitting a PPDU supporting a plurality of subchannels.

In an aspect, a method of transmitting a PPDU in a wirelesscommunication system is provided. The method includes selecting asubchannel among a plurality of subchannels, wherein a PLCP preamble anda PLCP header in each PPDU are independently generated in each of theplurality of subchannels, and transmitting a PPDU in the selectedsubchannel.

The PLCP header in the PPDU may comprise information on a modulation andcoding scheme (MCS) of the selected subchannel. The MCS of the selectedsubchannel may correspond to a MCS of a PLCP service data unit (PSDU) inthe PPDU.

A bandwidth of each of the plurality of subchannels may be 20 MHz. Thenumber of the plurality of subchannels may be four.

In another aspect, an apparatus for wireless communication includes aradio interface supporting a plurality of subchannels, and a processorcoupled with the radio interface and configured to select a subchannelamong the plurality of subchannels, wherein a PLCP preamble and a PLCPheader in each PPDU are independently generated in each of the pluralityof subchannels, and transmitting a PPDU in the selected subchannel.

In still another aspect, a method of transmitting a PPDU in a wirelesscommunication system is provided. The method includes generating aplurality of PPDUs in a plurality of subchannels, each of the pluralityof PPDUs comprising a PLCP preamble, a PLCP header and a PSDU, wherein aPLCP preamble and a PLCP header in each of the plurality of PPDUs areindependently generated in each of the plurality of subchannels, andtransmitting each of the plurality of PPDUs in each of the plurality ofsubchannels.

In a very high throughput (VHT) system consisting of a plurality ofsubchannels and having a channel bandwidth of 80 MHz or more, amodulation and coding scheme (MCS) or an error correction scheme is useddifferently in each subframe, and a physical layer convergence protocol(PLCP) protocol data unit (PPDU) is transmitted through each subchannel.Therefore, data can be effectively transmitted even if a legacy station(STA) coexists. According to an exemplary embodiment of the presentinvention, the MCS and the error correction scheme can be useddifferently in each channel when a channel characteristic issignificantly different from one subchannel to another. Therefore,channels can be effectively used.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view showing an exemplary structure of a wirelesslocal access network (WLAN) system according to an embodiment of thepresent invention.

FIG. 2 is a block diagram showing a multi-radio unification protocol(MUP) as an example of a protocol applicable to a very high throughput(VHT) system including a plurality of network interface cards (NICs)each having an independent radio interface.

FIG. 3 is a diagram showing a channel allocation mechanism of physicallayer convergence protocol (PLCP) protocol data units (PPDUs) in whichthe entirety of a bonding channel is regarded as one channel.

FIG. 4 is a diagram showing a channel allocation mechanism of PPDUsaccording to a first embodiment of the present invention.

FIG. 5 is a diagram showing a channel allocation mechanism of PPDUsaccording to a second embodiment of the present invention.

FIG. 6 is a diagram showing a channel allocation mechanism of PPDUsaccording to a third embodiment of the present invention.

FIG. 7 is a diagram showing a channel allocation mechanism of PPDUs,which is a detailed diagram of FIG. 4.

FIG. 8 is a block diagram of an apparatus for wireless communication.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 is a schematic view showing an exemplary structure of a wirelesslocal access network (WLAN) system according to an embodiment of thepresent invention.

Referring to FIG. 1, the WLAN system includes one or more basis servicesets (BSSs). The BSS is a set of stations (STAs) which are successfullysynchronized to communicate with one another, and is not a conceptindicating a specific region. A very high throughput (VHT) BSS isdefined as a BSS that supports a super high-speed data processing speedof 1 GHz or more.

A VHT system including one or more VHT BSSs can use a channel bandwidthof 80 MHz, which is for exemplary purposes only. For example, the VHTsystem may use a channel bandwidth of 60 MHz or 100 MHz or more. Assuch, the VHT system operates in a multi-channel environment where aplurality of subchannels having a specific size, e.g., a channelbandwidth of 20 MHz, are included.

The BSS can be classified into an infrastructure BSS and an independentBSS (IBSS). The infrastructure BSS is shown in FIG. 1. InfrastructureBSSs (i.e., BSS1 and BSS2) include one or more STAs (i.e., STA1, STA3,and STA4), access points (APs) which are STAs providing a distributionservice, and a distribution system (DS) connecting a plurality of APs(i.e., AP1 and AP2). On the other hand, the IBSS does not include APs,and thus all STAs are mobile STAs. In addition, the IBSS constitutes aself-contained network since connection to the DS is not allowed.

The STA is an arbitrary functional medium including a medium accesscontrol (MAC) and wireless-medium physical layer (PHY) interfaceconforming to the institute of electrical and electronics engineers(IEEE) 802.11 standard, and includes both an AP and a non-AP STA in abroad sense. A VHT STA is defined as an STA that supports the superhigh-speed data processing speed of 1 GHz or more in the multi-channelenvironment to be described below.

The STA for wireless communication includes a processor and atransceiver, and also includes a user interface, a display element, etc.The processor is a functional unit devised to generate a frame to betransmitted through a wireless network or to process a frame receivedthrough the wireless network, and performs various functions to controlSTAs. The transceiver is functionally connected to the processor and isa functional unit devised to transmit and receive a frame for the STAsthrough the wireless network.

Among the STAs, non-AP STAs (i.e., STA1, STA3, STA4, STA6, STAT7, andSTAB) are portable terminals operated by users. A non-AP STA may besimply referred to as an STA. The non-AP STA may also be referred to asa wireless transmit/receive unit (WTRU), a user equipment (UE), a mobilestation (MS), a mobile terminal, a mobile subscriber unit, etc. A non-APVHT-STA is defined as a non-AP STA that supports the super high-speeddata processing speed of 1 GHz or more in the multi-channel environmentto be described below.

The AP (i.e., AP1 and AP2) is a functional entity for providingconnection to the DS through a wireless medium for an associated STA.Although communication between non-AP STAs in an infrastructure BSSincluding the AP is performed via the AP in principle, the non-AP STAscan perform direct communication when a direct link is set up. Inaddition to the terminology of an access point, the AP may also bereferred to as a centralized controller, a base station (BS), a node-B,a base transceiver system (BTS), a site controller, etc. A VHT AP isdefined as an AP that supports the super high-speed data processingspeed of 1 GHz or more in the multi-channel environment to be describedbelow.

A plurality of infrastructure BSSs can be interconnected by the use ofthe DS. An extended service set (ESS) is a plurality of BSSs connectedby the use of the DS. STAs included in the ESS can communicate with oneanother. In the same ESS, a non-AP STA can move from one BSS to anotherBSS while performing seamless communication.

The DS is a mechanism whereby one AP communicates with another AP. Byusing the DS, an AP may transmit a frame for STAs associated with a BSSmanaged by the AP, or transmit a frame when any one of the STAs moves toanother BSS, or transmit a frame to an external network such as a wirednetwork. The DS is not necessarily a network, and has no limitation inits format as long as a specific distribution service specified in theIEEE 802.11 can be provided. For example, the DS may be a wirelessnetwork such as a mesh network, or may be a physical structure forinterconnecting APs.

FIG. 2 is a block diagram showing a multi-radio unification protocol(MUP) as an example of a protocol applicable to a VHT system including aplurality of network interface cards (NICs) each having an independentradio interface.

Referring to FIG. 2, an STA supporting the MUP includes a plurality ofNICs 110. The NICs 110 are separately depicted in FIG. 2, which impliesthat each NIC 110 may independently operate a MAC/PHY module. That is,the NICs 110 are distinctively depicted in FIG. 2 to show that the NICs110 are logical entities operating according to individual MAC/PHYprotocols. Therefore, the plurality of NICs 110 can be implemented withphysically distinctive functional entities, or can be implemented byintegrating the physical entities into one physical entity.

The plurality of NICs 110 can be classified into a primary radiointerface and one or more secondary radio interfaces. If a plurality ofsecondary radio interfaces are present, the secondary radio interfacescan be classified into a first secondary radio interface, a secondsecondary radio interface, a third secondary radio interface, etc. Theclassification into the primary interface and the secondary interfaceand/or the classification of the secondary ratio interface itself may bedetermined by a policy or may be adoptively determined in considerationof a channel environment.

The plurality of NICs 110 are integrally managed by the MUP 120. As aresult, the plurality of NICs 110 are externally recognized as if theyare one device. The VHT system includes a virtual-MAC (V-MAC) 130.Through the V-MAC 130, an upper layer 150 may ne recognize that amulti-radio channel is operated by the plurality of NICs 110. As such,in the VHT system, the upper layer 150 does not recognize themulti-radio channel through the V-MAC 130. This means that one virtualEthernet address is provided. A address resolution protocol (ARP) 160 isused to find a host's link layer address when only its Internet Layer(IP) or some other Network Layer address is known.

A physical layer convergence protocol (PLCP) sublayer interfaces thephysical layer (PHY) service to the IEEE 802.11 medium access control(MAC) service. A PLCP frame includes a PLCP preamble, a PLCP header, anda MAC management protocol data unit MPDU. The function of the PLCPsublayer is to provide a mechanism for transferring MPDUs between two ormore STAs.

A PLCP protocol data unit (PPDU) is a data unit in the PHY. The PPDUframe format provides for the asynchronous transfer of MAC sublayerMPDUs from any transmitting STA to all receiving STAs within thewireless LAN's BSS. The PPDU includes a PLCP preamble, a PLCP header,and a PLCP service data unit (PSDU). The PLCP preamble provides a periodof time for several receiver functions. These functions may includeantenna diversity, clock and data recovery, and field delineation of thePLCP header and the PSDU. The PLCP preamble may include information onsynchronization to be provided so that the receiver can perform thenecessary operations for synchronization. The PLCP header may be used tospecify the length of the whitened PSDU field and support any PLCPmanagement information.

Next, a channel allocation mechanism of PPDUs in a VHT system will bedescribed. Although the embodiments described below relate to a VHTsystem using a bonding channel in which contiguous 4 subchannels havinga bandwidth of 20 MHz are combined (i.e., a bonding channel having achannel bandwidth of 80 MHz), this is for exemplary purposes only. Theembodiments described below can equally apply to a VHT system includinga plurality of contiguous/non-contiguous subchannels (e.g., 3 or 5 ormore subchannels), which is apparent to those skilled in the art. Inaddition, the embodiments of the present invention are not limited tothe VHT system whose subchannel has a bandwidth of 20 MHz.

When a VHT system uses a bonding channel (having the channel bandwidthof 80 MHz) consisting of contiguous 4 subchannels (having a channelbandwidth of 20 MHz), a channel characteristic differs from onesubchannel to another. That is, not only a channel characteristicdiffers at a specific time but also a channel variation differs overtime. For example, a 1st subchannel with lowest frequency experiences nointerference, but a 4th subchannel with highest frequency may experiencedeterioration in its channel characteristic due to several factors. Inaddition, since a legacy STA exists only in a specific subchannel, thesubchannel needs to solve an interference problem caused by the legacySTA.

FIG. 3 is a diagram showing a channel allocation mechanism of PPDUs inwhich the entirety of a bonding channel is regarded as one channel.

Referring to FIG. 3, one PPDU is allocated through the entirety of thebonding channel consisting of 4 subchannels and is then transmitted to acounterpart VHT STA. In this case, a PLCP preamble and a PLCP header forPPDU transmission may also be transmitted by being allocated through theentirety of the bonding channel, instead of configuring themindependently for each subchannel. This mechanism is identical to achannel allocation mechanism of PPDUs in a WLAN system consisting of asingle channel, and thus can be easily used.

On the other hand, the mechanism of FIG. 3 does not consider a channelcharacteristic of each subchannel constituting the bonding channel, andthus there is a problem in that transmission efficiency is decreasedeven if a characteristic of any one of subchannels is poor. That is,since an error rate for a PPDU is determined by a subchannel having aworst channel characteristic, high transmission efficiency cannot beobtained even if a channel characteristic of another subchannel isexcellent. In this case, a modulation and coding scheme (MCS) and/or anerror correction scheme for the PPDU is also determined by thesubchannel having the worst channel characteristic. Therefore, accordingto the channel allocation mechanism of PPDUs of FIG. 3, there is alimitation in that subchannels having relatively good channelcharacteristics cannot be effectively used, and as a result,transmission efficiency of the entirety of the bonding channeldeteriorates.

To overcome the limitation, an embodiment of the present inventionproposes a channel allocation mechanism of PPDUs by considering anintrinsic characteristic of a VHT system in which respective channelcharacteristics of subchannels constituting a bonding channel aredifferent and flexible.

According to the embodiment of the present invention, a PLCP preambleand/or a PLCP header may be generated independently in each subchannel.By doing so, an MCS and/or an error correction scheme (e.g., a forwarderror correction (FEC) such as low density parity check (LDCP) or ReedSolomon code) for subsequent PPDU transmission can be used differentlyin each subchannel.

FIG. 4 is a diagram showing a channel allocation mechanism of PPDUs in aVHT WLAN system according to an embodiment of the present invention.

Referring to FIG. 4, ‘single PPDU’ denotes a time interval to transmitone PPDU. A first PPDU (PPDU1), a second PPDU (PPDU2) and a third PPDU(PPDU3) are subsequently transmitted. Each PPDU is transmitted over 4subchannels and may have different MCS in each subchannel. This meansthat each PPDU may have multiple portions which are independentlygenerated in each subchannel. Each portion may include a PLCP preambleand/or a PLCP header. The PLCP header may include the MCS whichcorresponds to a MCS of a PSDU in the each portion.

FIG. 5 is a diagram showing a channel allocation mechanism of PPDUs in aVHT WLAN system according to another embodiment of the presentinvention. The embodiment of FIG. 5 relates to a method of PPDUaggregation for point-to-point connection.

Referring to FIG. 5, a first PPDU (PPDU1), a second PPDU (PPDU2), athird PPDU (PPDU3) and a fourth PPDU (PPDU4) are simultaneouslytransmitted but are transmitted in different subchannels. One PPDUoccupies one subchannel. Therefore, each PPDU is independently generatedin each subchannel and may have different MCS. If N is the number ofsubchannels, up to N PPDUs can be simultaneously transmitted.

A STA may use a plurality of subchannels or one of the plurality ofsubchannels. Before transmit a PPDU, a STA may receive information onthe selected subchannel from an AP. The AP may indicate each subchannelto be used by each STA.

According to this embodiment, an MCS and/or an error connection schemecan be used differently for each PPDU. That is, since transmission isperformed using independent subchannels for each PPDU, any MCS and/orerror correction scheme can be used for each PPDU. For example, an MCSand an error correction scheme having a relatively smaller amount ofadditional data derived from the MCS and/or the error correction schemecan be used for a subchannel whose channel characteristic is excellentat a specific time. An MCS and/or an error correction scheme capable ofensuring successful PPDU transmission even if a channel condition ispoor may be used for a subchannel whose channel characteristic is poor.If a legacy STA operates in a specific subchannel and the legacy STAoccupies the subchannel, a PPDU may be not transmitted through thesubchannel.

In order to allocate the PPDU for each subchannel in this manner,relevant information is preferably reported in advance to a counterpartVHT STA by using a previously transmitted PLCP preamble and/or PLCPheader. That is, by using the PLCP preamble and/or PLCP header,information regarding signal detection, automatic gain control (AGC),diversity selection, channel and fine frequency offset estimation and/oran MCS and error correction scheme is reported to a recipient VHT STA.

In addition, for the effective use of a method of transmitting a PPDUindependently for each subchannel according to the embodiment of thepresent invention, that is, a method of PPDU aggregation forpoint-to-point connection, a transmission time of PPDUs transmitted atthe same time is maintained to be as identical as possible. As such, tomaintain the transmission time of PPDUs transmitted through differentchannels, it is preferable to adaptively regulate a size of a PPDUtransmitted through one subchannel by property fragmenting the PPDU orby using a zero padding or the like.

FIG. 6 is a diagram showing a channel allocation mechanism of PPDUs in aVHT WLAN system according to another embodiment of the presentinvention. The embodiment of FIG. 6 relates to a method of PPDUaggregation for point-to-multipoint connection.

If a legacy STA accesses to a VHT AP, the use of a channel allocationprocedure of PPDUs as shown in FIG. 4 may result in deterioration ofoverall performance of a VHT BSS managed by the VHT AP and deteriorationof a data transmission throughput. This is because, in a VHT WLAN systemusing a bonding channel including a plurality of subchannels, if thelegacy STA uses only any one of subchannels, for example, if a legacyIEEE 802.11 STA uses only a channel bandwidth of 20 MHz in a VHT BSSusing a channel bandwidth of 80 MHz, the use of the channel allocationmechanism of PPDUs as shown in FIG. 4 results in discarding othersubchannels (i.e., a 60 MHz channel).

According to one method of solving these problems, in a VHT WLAN systemaccording to the embodiment of the present invention, differentsubchannels are used when a legacy IEEE 802.11 STA accesses to a VHT AT.In this case, if one or more legacy STAs are connected to the VHT AP,irrespective of whether it is a VHT STA or a legacy STA, another STA canbe configured to use one or more subchannels different from those of thepreviously connected legacy STA.

For example, as shown in FIG. 6, separate 4 legacy STAs (i.e., a legacySTA 1, a legacy STA 2, a legacy STA 3, and a legacy STA 4) can access toa VHT-AP by using corresponding separate subchannels (e.g., a subchannel1, a subchannel 2, a subchannel 3, and a subchannel 4 respectively forthe legacy STAs 1, 2, 3, and 4). For this, the VHT-AP is preferablyallowed to independently transmit a probe response frame and/or a beaconframe or the like with respect to all subchannels.

Assume that a VHT AP transmits frames to legacy STAs. In this case, theVHT AP constitutes a bonding channel and transmits the frames to eachlegacy STA by using subchannels connecting the legacy STAs. If the VHTSTA uses a channel bandwidth of 80 MHz, the frames can be transmitted toup to the 4 legacy STAs by fully using the 80 MHz channel. In this case,a PPDU for each legacy STA is transmitted by using independentsubchannels. If N is the number of subchannels, up to N legacy STAs canperform transmission simultaneously.

According to the embodiment of the present invention, any MCS and/orerror correction scheme is used in each legacy STA using an independentsubchannel. That is, according to the embodiment of the presentinvention, legacy STAs using different subchannels may use different MCSand/or error correction schemes. In order to allocate the PPDU for eachsubchannel in this manner, relevant information is preferably reportedin advance to a counterpart VHT STA by using a previously transmittedPLCP preamble and/or PLCP header. That is, by using the PLCP preambleand/or PLCP header, information regarding signal detection, automaticgain control (AGC), diversity selection, channel and fine frequencyoffset estimation, and/or MCS and error correction scheme is reported toa recipient VHT STA.

FIG. 7 is a diagram showing a channel allocation mechanism of PPDUsaccording to the embodiment of the present invention described abovewith reference to FIG. 4. Referring to subfigure (a) of FIG. 7, one PPDU(e.g., PPDU1, PPDU2, PPDU3, and PPDU4) is transmitted through theentirety of a bonding channel. However, according to the embodiment ofthe present invention, an MCS or an error correction scheme or the likecan be used differently in each subchannel by considering a channelcharacteristic of each subchannel. Referring to subfigure (b) of FIG. 7,one PPDU is allocated for each subchannel and is then sequentiallytransmitted. That is, one PPDU is not transmitted through a plurality ofsubchannels.

FIG. 8 is a block diagram of an apparatus for wireless communication. Anapparatus 800 includes a radio interface 810 and a processor 820. Theapparatus 800 may be a part of a STA or an AP. The radio interface 810may support a plurality of subchannels. The radio interface 810 maytransmit a radio signal over at least one of the plurality ofsubchannels. The processor 820 is coupled with the radio interface 810and transmits at least one PPDU via the radio interface 810. The method,procedure, mechanism and functions described in this disclosure may beimplemented by the processor 820. The processor 820 may independentlygenerate PPDUs in subchannels.

Method steps may be performed by one or more programmable processorsexecuting a computer program to perform functions by operating on inputdata and generating output. Method steps also may be performed by, andan apparatus may be implemented as, special purpose logic circuitry,e.g., an FPGA (field programmable gate array) or an ASIC(application-specific integrated circuit).

Although the present invention has been particularly shown and describedwith reference to exemplary embodiments thereof, it will be understoodby those skilled in the art that various changes in form and details maybe made therein without departing from the spirit and scope of theinvention as defined by the appended claims.

What is claimed is:
 1. A method of transmitting a physical layerprotocol data unit (PPDU) in a wireless communication system, the methodperformed by a wireless device and comprising: for a first data streamassociated with a first PPDU to be transmitted via a first channel,including a first data block, a first header and a first physical layerservice data unit (PSDU) in the first data stream, wherein the firstheader indicates a modulation and coding scheme (MCS) of the first PSDU;for a second data stream associated with a second PPDU to be transmittedvia a second channel, including a second data block, a second header anda second PSDU in the second data stream, wherein the second headerindicates an MCS of the second PSDU; performing a padding procedure toat least one of the first data stream and the second data stream so thata time duration during which the first data stream is transmitted and atime duration during which the second data stream is transmitted have anequal time duration; and transmitting the first data stream and thesecond data stream by using the first PPDU and the second PPDU.
 2. Themethod of claim 1, wherein the first data block and the second datablock include information on synchronization.
 3. The method of claim 1,wherein the first channel and the second channel are determined based oncontrol signaling received from an access point (AP).
 4. The method ofclaim 1, wherein the first PPDU is used for a first receiver and thesecond PPDU is used for a second receiver.
 5. A wireless device fortransmitting a physical layer protocol data unit (PPDU) in a wirelesscommunication system, the wireless device comprising: a processorconfigured to: for a first data stream associated with a first PPDU tobe transmitted via a first channel, include a first data block, a firstheader and a first physical layer service data unit (PSDU) in the firstdata stream, wherein the first header indicates a modulation and codingscheme (MCS) of the first PSDU, for a second data stream associated witha second PPDU to be transmitted via a second channel, include a seconddata block, a second header and a second PSDU in the second data stream,wherein the second header indicates an MCS of the second PSDU, andperform a padding procedure to at least one of the first data stream andthe second data stream so that a time duration during which the firstdata stream is transmitted and a time duration during which the seconddata stream is transmitted have an equal time duration; and atransmitter configured to transmit the first data stream and the seconddata stream by using the first PPDU and the second PPDU.
 6. The wirelessdevice of claim 5, wherein the first data block and the second datablock include information on synchronization.
 7. The wireless device ofclaim 5, wherein the first channel and the second channel are determinedbased on control signaling received from an access point (AP).
 8. Thewireless device of claim 5, wherein the first PPDU is used for a firstreceiver and the second PPDU is used for a second receiver.